The definition of Sino-US diplomacy has become blurrier and more confusing. In the past we believed that it meant the leaders of both countries visited each other, talking about trade or military affairs. Now many have realized that “Sino-US diplomacy” has also been underlying in the frictions in the South China Sea and the Diaoyu Islands, as well as the Korean Peninsula. The role the US has been playing in these areas make China uneasy.

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A large number of Chinese believe the ultimate goal of the US government is to overturn the current political system here, just as many believe it did with the Soviet Union.

On the other hand, the US has been sensitive about Chinese moves. The US is anxious over China’s economic growth as well as its military expenditure. China catching up to the US in terms of overall strength is also making leaders there uncomfortable.

Will this anxiety turn into real action to contain China? This remains uncertain. But many Chinese refer to the frictions between the US and China as signs of a US intent to move in that direction.

US secretary of state John Kerry met Chinese president Xi Jinping and other senior leaders in Beijing, saying afterwards: “We are able … to underscore our joint commitment to the denuclearisation of the Korean peninsula in a peaceful manner.”

Standing alongside China’s top diplomat, state councillor Yang Jiechi, he added: “We agreed that this is critically important for the stability of the region and indeed for the world and for all of our nonproliferation efforts.”

Yang said: “We maintain that the issue should be handled and resolved peacefully through dialogue and consultation. To properly address the Korea nuclear issue serves the common interests of all parties. It is also the shared responsibility of all parties.”

To American ears, something new was said Saturday in the Communist Party’s walled leadership compound in central Beijing: China agreed to join the rest of the international community in pressuring North Korea to give up its atomic weapons program.

But while that would be a welcome breakthrough as apprehension continues to grow in and around the two Koreas, it’s not quite the case, at least not yet.

Despite Mr. Kerry’s optimism, the language of the Chinese statements after the Saturday meetings was the same as it has been for years. The problem should be resolved through dialogue, Beijing insisted, preferably via the six-party talks that have been dormant since 2007.

Kerry left Beijing with no joint statement from the Chinese warning North Korea to cease its threats; indeed, Chinese officials wouldn’t even mention the country by name as they alluded to “challenges we face on the Korean peninsula.” That’s a delicate way of putting that the entire region is bracing for yet another North Korean missile launch, perhaps as soon as Monday, as experts debate whether it’s months or years before Pyongyang has the capability of delivering a nuclear warhead atop a missile.

As for the “tough message” that State Department officials have said Kerry would urge Beijing to send to North Korea, there was no evidence of that happening, and analysts said they wouldn’t count on it – the Chinese are worried about pushing too hard on Kim Jong Un, an inexperienced and capricious young dictator whose only end game appears to be regime survival. The situation is just too precarious, analysts said, for China to leverage its huge aid and investments in exchange for, say, a return to multilateral negotiations with the goal of Kim scrapping his nuclear program.

“American expectations may be too high,” said Robert Ross, a professor of Chinese foreign policy at Boston College. “Here we’re asking for greater Chinese economic pressure from North Korea at the very time when China is most concerned about stability in North Korea.”

In fact, on North Korea, too, China is offering few signs of a fundamental shift in its stance. Short-term interests converge. Neither America nor China wants a war. Both seem to regard Kim Jong Un as an unhinged teenager who needs to be back on his meds. But in the long run, America worries more about a nuclear-armed North Korea. China worries about the country’s collapse. An article this month in Global Times, a Communist Party newspaper, by Zhu Zhangping, an “independent observer”, noted the danger North Korea’s nuclear tests—just over 100km (60 miles) from the Chinese border—pose to China’s water supply and the safety of its food. But, he argued, “North Korea still acts as a buffer.” Were it to collapse, American troops would be at China’s frontiers, and hordes of refugees might flood across the border. China has to “ensure the Kim regime’s survival.”

North Korea has a clear choice available, Mr. Kerry said, according to The Associated Press, and will find “ready partners” in the United States if it follows through. The Japanese foreign minister, Fumio Kishida, was more specific, saying that Pyongyang must meet its commitment to earlier deals regarding its nuclear and missile programs and on returning kidnapped foreigners.

China’s cooperation is essential to the Obama administration’s strategy of holding a tough line on Pyongyang in an attempt to achieve the type of long-lasting solution on the nuclear program that has eluded a string of United States presidents. Previous administrations responded to North Korean provocations by eventually offering aid to tamp down tensions, only to see the North’s promises to relinquish its nuclear program evaporate once the aid had been delivered.

The relationship between North Korea and China, extolled in the past to be as close as “lips and teeth,” has faltered ever since as Mr. Kim, a political neophyte believed to be in his late 20s, has continued to defy Mr. Xi, a 59-year-old seasoned statesman.

How far the alliance between the powerhouse China and the impoverished North Korea has soured is now debated openly in the Chinese news media. Few call it a serious rift, though a spirited debate appears to be under way within the Chinese government over how to handle Mr. Kim.

But with Secretary of State John Kerry in China this weekend on his first visit as the United States’ chief diplomat, some things are clear.

The personal relationships among Mr. Kim and his Chinese counterparts appear to be less familiar than when his father, Kim Jong-il, was in charge. Analysts suggest that could be a result of the significant age differences between the inexperienced Mr. Kim and the much older Chinese leaders.

Speaking to reporters in Beijing during a visit to China, Kerry said the United States and China had agreed on the need to speed up action on cyber security, an area that Washington says is its top national security concern.

Cyber security, Kerry said “affects the financial sector, banks, financial transactions, every aspect of nations in modern times are affected by the use of cyber networking and obviously all of us – every nation – has an interest in protecting its people, protecting its rights, protecting its infrastructure”.

Earlier, China’s official Xinhua news agency quoted Foreign Minister Wang Yi as telling Kerry in their meeting that China and the United States should make joint efforts to safeguard cyberspace.